1. Field of the Invention
The present invention relates to an optical disk device, and more particularly to a device for reading data from a rewritable optical disk.
2. Description of the Prior Art
The conventional optical disk device and data management method will be described by reference to FIG. 4 and FIG. 5. FIG. 4 is a diagram showing the conventional system configuration, and FIG. 5 is a diagram showing the configuration of conventional optical disk and optical disk device. As shown in FIG. 4 and FIG. 5, the conventional technology includes an optical disk device 10 which acquires data of a rewritable optical disk and stores it temporarily (this process will be referred to as buffering and also as buffer for short) and a host computer 1 which is the eventual transfer destination of the buffered data
In the discussion that follows, a pointer within a cache of a cached alternate area will be represented as a cache pointer. Moreover, a list consisting of a plurality of sets each of which being formed of an address in a defective area and a cache pointer will be represented as a cache table 45, and a pointer showing the position in a temporary storage memory area 41 of an alternate list for the cache table 45 will be represented as a table pointer.
The optical disk device 10 is composed of a rewritable optical disk (represented as ReWritable optical disk in the drawings) 2 having an alternate list 11, a data area 12 and an alternate area 13, a decoder 3 for acquiring data from the optical disk 2, a temporary storage memory area 5, and a control unit 4 for controlling data acquisition, construction of a cache table and transfer of data to the host computer 1.
The decoder 3 acquires an alternate list 44 from the optical disk 2 for the alternate list temporary storage memory area 41, executes buffering for the data area 12, and executes caching for a data in the alternate area 13.
The temporary storage memory area 5 is subdivided into an alternate list temporary storage memory area 41 for buffering the alternate list 11, a data temporary storage memory area 43 for buffering data, and a cache 42 for caching a data in the alternate area.
The operation of the prior art will be described by reference to FIG. 5 and FIG. 6. FIG. 6 is a flowchart showing data buffering flow according to the conventional technology.
1. Acquisition of the Alternate List (S1 and S2)
The control unit 4 designates an address of the alternate list 11, an acquisition destination pointer of the alternate list, and the acquisition size of the alternate list to the decoder 3 (S1), and the decoder 3 acquires, for the alternate list acquisition destination pointer of the alternate list temporary storage memory area 41, an alternate list 11 from the address of the designated alternate list 11 of the optical disk 2 for the portion corresponding to the alternate list acquisition size (S2).
2. Buffering of the Data Area 12 (S23 and S24).
The control unit 4 designates the address of the data area 12, the buffer pointer and the buffer size to the decoder 3 (S23), and the decoder 3 executes buffering to the buffer pointer for the portion corresponding to the buffer size, from the address of the designated data area 12 of the optical disk (S24).
3. Caching of Data in the Alternate Area 13 (S25 to S30)
The control unit 4 retrieves within the alternate list 11 to check whether or not there exists a defective data in the buffering data (S25). If no defective data exists, caching of data in the alternative area 13 will not take place (S26) If there exists one, it is checked whether or not the alternate area 13 required for caching has already been cached (S27), and only when it is not cached yet, the control unit 4 designate the address, the caching size and the cache pointer of the alternate area 13 to the decoder 3 (28), and the decoder 3 caches, to the cache pointer, data of the alternate area 13 for the portion corresponding to the cache size from the addresses of the alternate area 13 (S29).
Moreover, with an address of a defective area and a buffer pointer where the data of the defective area is buffered are formed into one set, a cache table 45 is constructed from a collection of such sets equal in number to the number of buffer pointers present in the area of the temporary storage memory area 5 (S30).
4. Transfer of Buffered Data and Cached Data to the Host Computer (S31 to S34)
The control unit 4 checks whether or not the buffered data indicated by the buffer pointer is a defective data by referring to the caching table constructed in process 3 in the above (S31). If it is not defective, data is transferred from the temporary storage memory area 5 to the host computer 1 (S33), and if it is a defective data, an alternate data for the defective data is transferred to the host computer 1 from the cache (S32). The above processing is repeated for number of times corresponding to the buffer size (S34).
As seen from the above processing, when a defective data is found in the data buffered from a rewritable optical disk, it is necessary to cache alternate area data to serve as the substitute. Prior art for caching an alternate area can be found in Japanese Patent Applications Laid Open, No. 2000-21090, Japanese Patent Applications Laid Open, No. 2000-298949, Japanese Patent Applications Laid Open No. Hei 6-325494, Japanese Patent Applications Laid Open, No. Hei 8-180598, Japanese Patent Applications Laid Open, No. Hei 1-245463, and the like. However, a cache is needed for implementing caching, which has been a problem in the method.
That is, a rewritable optical disk has an alternate list and an alternate area in the unit of tracks, and access is made in the unit of tracks, so that according to the conventional method, caching algorithm fails to act effectively, and an additional caching time and a cache are needed for implementing caching.